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Dark Streaks on Mars Suggest Running Water Still Present
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
11 December 2002
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Dark surface streaks along canyon and crater walls on Mars could be signs of running water presently scouring the surface, according to a new study. The streaks occur in areas thought by some scientists to involve long-running thermal activity under the surface. The salty water seeps to the from below, now and then, because of interactions with hidden, hot, molten rock, the thinking goes.The process is thought to operate somewhat like an ephemeral hot spring on Earth.The research was presented this week at a meeting of the American Geophysical Union in San Francisco. It does not by any means represent the final word on the possibility for water on Mars. More evidence would be needed to confirm whether some of the streaks were in fact created by water.Mars is known to contain significant quantities of waterice. But there have been no firm detections of liquid water, a key requirement for life, as we know it. Meanwhile, other scientists at the meeting have been portraying the Red Planet as cold and dry.Another recent study suggested Mars has quite possibly had a lifeless history, despite the hope of many scientists that liquid water and signs of life will eventually be found.The study of Mars is never boring. New life for old idea The new study is not the first to hold the dark streaks up as signatures of running water. The Viking missions of the 1970s first spotted them, and scientists then suggested they might have been caused by water. Other researchers said wind, dust or landslides might be responsible, and the idea that water was at work lost favor over the years."There is no identifiable characteristic of a dark slope streak that can definitively say whether it was formed by water-related processes or not,"said Justin C. Ferris, National Research Council Postdoctoral Fellow at the U.S. Geological Survey in Denver, Colo. "But there are certainly some features which strongly suggest the role of water."Ferris and his colleagues -- James Dohm, Victor Baker, and Tom Maddock, all of the University of Arizona -- acknowledge that wind and other erosion are responsible for some of the streaks. Their study shows that streaks have been observed to fade in mere decades. Others are new, having appeared after the Mars Global Surveyor spacecraft began detailed mapping of the planet in April of 1999. "These are definitely minor seepage," Ferris told SPACE.com. "But they're occurring as we speak, which is what makes them exciting."Over the past two years, photos of layeredsediments and other erosionalfeatures have been attributed to possible water flows in the relatively recent geologic past of Mars by other scientists. But this week's announcement is among the few suggestions for evidence of surface water that might exist now.The evidence A handful of characteristics regarding the streaks suggest water is involved.The streaks often originate at or near seams between two types of rock, the new analysis shows. They tend to occur on valley walls and continue down to the valley floor. Perhaps most important, the features do not crop up in all locations with similar slope and material, which would be expected if only wind or landslides were responsible."Interestingly, most regions that contain dark slopestreaks show evidence of ground ice or water and magma interactions," saidDohm, a geologist who has also mapped scenarios for colossalwater flows on ancient Mars.While there is no doubt that volcanic activity was once common on Mars, Dohm's suggestion that hot magma might lurk just below the surface today has not been proven.Salty water freezes at lower temperatures and might remain in the liquid phase at the surface of the chilly planet, the researchers say."Thus, the briny water could flow slowly down slope, leaving behind a ghostly image that we call a dark slope streak," Ferris said. "This hypothesis implies that there is current hydrological activity on the surface of Mars." The darkness might be caused by water washing away lighter-colored surface material, or it could be a result of saturated soil.The scientists suggest that the dark streaks would make good places for further study, including possible sample-return missions. They also are aware that the search for possible water on Mars is ultimately also a search for possible life."And where you have a long-lived heat source and ample water, there is an exciting potential for subsurface life," Dohm said.The10 Best Mars Images EverMore Mars News
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